JsxGraph from Dart using Dart JS interop
There's a jsify missing in your code:
JsObject jsxGraph = context['JXG']['JSXGraph'];var board = jsxGraph.callMethod('initBoard', [ 'box', new JsObject.jsify({ 'boundingbox': [-10, 10, 2, -1], 'axis': true, 'keepaspectratio': false, 'showNavigation': false })]);var graph = board.callMethod('create', [ 'functiongraph', new JsObject.jsify([(x){return 3*x*x + 5*x + 1;}, -10, 10]}, new JsObject.jsify({'strokeColor': '#ffff00'})]);